Wednesday, November 12, 2008

Titan ICBM

Titan II on display at the National Museum of the US Air Force, July 2012

Although Minuteman I had signaled the start of a trend towards smaller, lower-yield strategic weapons, there remained a need for a new heavy ICBM with multi-megaton capability, and Martin was contracted to work on just such a weapon in June 1960 using the Titan I as a basis. The missile that emerged from this program, the SM-68B/LGM-25C Titan II was a thoroughly redesigned vehicle, although the same basic engines would be used.Structurally, Titan II was externally distinguishable by its revised second stage, which was now as wide as the first. Completely new armament was fitted as well, in the form of a nine-megaton yield W53 device housed in a Mk.6 RV built by General Electric and similar to an earlier test article that had been launched by an Atlas.In order to maximize survivability, Minuteman-type silo basing was imperative. Although subscale tests had been carried out, the Titan silo concept had to be tested “under fire” and to facilitate this, a representative silo was built at Vandenberg. As a Titan II was not yet available by the spring of 1961, an HGM-25 was used instead for the first silo launch. On May 3, 1961 the test took place, with the great “W”-shaped flame deflector underneath the missile venting flames and exhaust away; the silo walls themselves were coated with material to keep acoustic vibrations from being reflected back onto the missile. As the sole purpose of the test was to validate silo launching, a full-range shot was not needed, and the missile (with an inert upper stage) was intentionally destroyed shortly into the flight.Titan II also had to achieve a launch readiness in the range of sixty seconds or so, far less than Titan I or any Atlas variant. This ruled out fueling the missile after an alert had been received, and the need for a storable liquid fuel was met by switching to non-cryogenic Unsymetrical Dimethyl Hydrazine and Anhydrous Hydrazine. The new fuels were hypergolic (self-igniting) which simplified the engine design, but made leakage a critical problem. The first stage LR87 engines were retained, but in uprated -AJ-5 form , each being rated at 215,000lbs of thrust. The second-stage LR-91-A-5 was upgraded as well, to a 100,000lb thrust rating.

Titan II engines at NMUSAF, July 2012

Some LGM-25C procurement plans called for around 100 silos, but this figure was halved as Minuteman became the predominant US ICBM. In 1967 it was announced that no further Titan IIs would be produced or deployed; this decision would later result in a lack of missiles for testing an training launches when the system ended up being kept in service long past the expected retirement date. Titan II squadrons would be based at Little Rock AFB, Arkansas, Davis-Monthan AFB, Arizona, and McConnell AFB, Kansas; a total of 54 silos were built. The Titan II's great physical size meant that a substantial number of smaller warheads as well as penetration aids could have been carried instead of the single large RV, and studies on such configurations were carried out. However, the limited deployment and anticipated short service life of the LGM-25C meant that no new payloads were put into service.The Titan II's propulsion system was to cause a deal of trouble of the lifetime of the system. Even beyond the absolute need to keep the fuels apart, the propellants were also incredibly toxic, necessitating extreme care when working around a fueled missile. Titan II's problems were evident from early on, and some proposed to retire the system by as early as 1972. However, the type was retained in service, as by the late 1970s it was one of the few multi-megaton nuclear weapons in active service, and could be assigned to take out very hardened or otherwise very important targets. Keeping the old missiles operational meant that aging subsystems needed replacement, and the force was backfitted with the Universal Space Guidance System to take the place of the original inertial set, which was becoming increasingly unsupportable. A major accident at a Little Rock AFB silo near Searcy, Arkansas occurred on August 9, 1965, when a fire began while civilian workers were in the facility. The warhead had been removed, but the missile remained fueled, leading to fears that the blaze could lead to a huge explosion. This did not happen, but dozens of men were trapped within the silo, and the death toll reached 53. Another accident, this time at a Davis-Monthan silo, occurred on March 23, 1966 when an oxidizer leak forced evacuations.1978 saw more Titan accidents; on January 27, a fuel leak at a Damascus, Arkansas silo forced some civilians living nearby to evacuate, but the launch team was able to stay on duty. Much more serious was a mishap in late August at a silo near Rock, Kansas, outside of Wichita. During an oxidizer refuelingoperation, fumes from a leak killed one airman and forced hundreds of nearby civilians to leave their homes. It was necessary to pump tens of thousands of water into the silo, although this in turn led to nitric acid being formed from the combination of H2O and oxidizer.Although not the costliest in terms of lives lost, a Titan accident in Arkansas in the early fall of 1980 was probably the most public of the system's mishaps, with much public attention thereafter being focused on the system. The accident began on the evening of September 18, during maintenance on Silo 374-7's missile. Encumbered by the environmental suit necessary in the silo, a worker dropped a wrench socket and the three pound tool hit the side of the missile with sufficient force to pierce the skin and gash a fuel tank. Escaping fumes soon forced the crew to evacuate the silo, and after a water suppression system failed to quell the emergency, the control center team was also forced to leave. An emergency team was sent out to secure the facility and attempt to stop the leak. Entry was made, but extremely high vapor levels dictated evacuation. Just before the team could exit the complex, the fumes ignited, triggering a massive explosion that obliterated the missile, blew the 700+ ton silo cover off, and threw the RV hundreds of feet into the air. Both the men caught in the blast were seriously injured, and one later died from his wounds. Although the warhead had landed within the bounds of the site, debris from the explosion was found at least a mile away. The intact but dented RV/warhead was found some hundreds of feet from the remains of the silo, although sticking to the official policy of not confirming the presence or absence of nuclear weapons, the USAF initially declined to officially state that the recovery had taken place. After being rendered safe for transport, the warhead was taken to the nuclear weapons plant at Pantex, Texas.Although the disaster at 374-7 would be the last major Titan II accident, further incidents with the system were to take place including one two months later when a pair of Davis-Monthan sites experienced chemical leaks. By the time of the Damascus accident, the surviving Titans were almost a decade past their projected retirement date, and maintenance costs associated with an aging specialist system were substantial. Coupled with the various accidents, this led to a decision in 1981 to phase out the old missiles, although the withdrawal would be a gradual one, allowing some Titans to remain online until newer systems were ready. The decommissioning program, codenamed Rivet Cap, got underway when a missile was taken from a Davis-Monthan silo.

Withdrawal

The withdrawal ended in the summer of 1987 when the 308th SMW pulled its last missile, leaving the US without a liquid-fueled ICBM. The final phase out actually came at a good time for the US space program, which at the time was suffering from a shortfall of boosters due to groundings following accidents that had occurred with the Shuttle and Titan 34 programs; at the same time, the supply of former Atlas ICBMs was finally beginning to dwindle. Martin (later Lockheed-Martin) received a contract in early 1986 to refit an initial batch of Titan IIs to Space Launch Vehicle (SLV) configuration. Titan II airframes remain in storage at the Aerospace Materials And Recovery Center (AMARC) at Davis-Monthan AFB, near where some of them sat operational alert. One Davis-Monthan silo has been dedicated as a museum, complete with a “neutered” missile.Decades before the Titan SLV flew, the basic missile had played an important part in early US manned spaceflight, serving as the launcher for NASA's two-man Gemini capsules. Man-rating the vehicle did pose some problems, as the solution to a longitudinal oscillation had to be found. Titan II also spawned a whole family of specialized space launch derivatives. The Titan 3A was basically a Titan II with an upper stage, but all subsequent launchers have stemmed from the Titan 3B configuration, which added a pair of large strap-on solid boosters. This was also seen as a potential weapons system, especially for FOBS and other special payloads, but development of a weaponized version did not go ahead.
Titan II resin model kit from Anigrand

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